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Steel sheet excellent in workability and method for producing the same

a technology of steel sheets and workability, applied in the field of steel sheets, can solve the problems of deterioration of secondary workability, substantial negative effects on the conservation of the global environment, and deterioration of weldability and fatigue strength, and achieve good r-values and methods of production, without incurring a high cost and burdening the global environment excessively, and high strength.

Inactive Publication Date: 2008-07-10
NIPPON STEEL CORP
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

[0010]The present invention relates to providing a steel sheet and a steel pipe having good r-values and methods for producing them without incurring a high cost and burdening the global environment excessively, the steel sheet being a high strength steel sheet having good formability while containing a large amount of C.
[0011]Another object of the present invention is to provide a steel sheet having yet better formability and a method for producing the steel sheet without incurring a high cost.
[0012]Still another object of the present invention is to provide a high strength steel sheet and steel pipe containing a large amount of C, having good deep drawability and containing bainite, martensite, austenite and the like, as required, other than ferrite.
[0013]Yet another object of the present invention is to provide a high strength steel sheet, while containing comparatively large amounts of C and Mn, having good deep drawability without incurring a high cost and burdening the global environment excessively.

Problems solved by technology

Emitting the CO2 gas is not environmentally friendly and may have substantial negative effects as to the conservation of the global environment.
However, the disclosed steel contains P in quantity, thereby causing the deterioration of secondary workability, problems with weldability and fatigue strength after welding in some cases.
However, such a steel pipe finished through high-temperature processing often contains solute C and solute N in quantity.
These solute elements sometimes cause cracks to be generated during hydroforming and surface defects such as stretcher strain may be induced.
Other problems with such a steel pipe include deteriorated productivity due to high-temperature thermo-mechanical treatment applied after a steel sheet has been formed into a tubular shape, negative effects on the global environment, increased cost, and the like.

Method used

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Examples

Experimental program
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Effect test

embodiment 1

[0021]According to an exemplary embodiment of the present invention a steel sheet or steel pipe having particular chemical components is provided. C is effective for strengthening steel and the reduction of the amount of C in steel causes cost of making the steel to increase. For these reasons, a C amount is set at 0.08% or more of the mass of the steel. Meanwhile, an excessive addition of C is undesirable for obtaining a good r-value, and therefore the upper limit of C is set at 0.25% of the mass of the steel. It should be noted that the r-value of the steel is improved when the amount of C is reduced to less than 0.08% of the mass of the steel. However, reduction of the amount of C to such a low amount is excluded due to other negative side effects of such reduction. A preferable range of an amount of C is from approximately more than 0.10 to 0.18% of the mass of the steel.

[0022]Addition of Si increases the mechanical strength of steel economically and thus it may be added to achi...

embodiment 2

[0065]According to another exemplary embodiment of the present invention, a steel sheet or steel pipe having particular chemical components is provided C is effective for strengthening steel and the reduction of the amount of C causes cost to increase. Besides, by increasing the amount of C, it becomes easy to make the metallographic microstructure of a hot-rolled steel sheet composed mainly of bainite and / or martensite. For these reasons, C is added proactively. An addition amount of C is set at approximately 0.03 mass % or more. However, an excessive addition of C is undesirable for securing a good r-value and weldability and therefore the upper limit of an amount of C is set at approximately 0.25 mass %. A desirable range of the amount of C is from approximately 0.05 to 0.17 mass %, and more desirably approximately 0.08 to 0.16 mass %.

[0066]Si raises the mechanical strength of steel economically and thus it may be added in accordance with a required strength level. Further, Si al...

embodiment 3

[0092]According to still another embodiment of the present invention, a steel sheet or steel pipe having particular chemical components is provided. C is effective for strengthening steel and the reduction of a C amount causes cost to increase. For these reasons, a C amount is set at approximately 0.04 mass % or more. Meanwhile, an excessive addition of C is undesirable for obtaining a good r-value, and therefore the upper limit of a C amount is set at approximately 0.25 mass %. A preferable range of a C amount is from approximately 0.08 to 0.18 mass %.

[0093]Si raises the mechanical strength of a steel economically and thus it may be added in accordance with a required strength level. Further, Si is effective for fractionizing carbides and equalizing a metallographic microstructure in a hot-rolled steel sheet, and resultantly has the effect of improving deep drawability. For these reasons, it is desirable to add Si by approximately 0.2 mass % or more. On the other hand, an excessive...

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Abstract

The present invention provides a steel sheet excellent in workability, which may be used for components of an automobile or the like, and a method for producing the same. More specifically, according to one exemplary embodiment of the present invention, a steel sheet excellent in workability, including in mass, 0.08 to 0.25% C, 0.001 to 1.5% Si, 0.01 to 2.0% Mn, 0.001 to 0.06% P, at most 0.05% S, 0.001 to 0.007% N, 0.008 to 0.2% Al, at least 0.01% Fe. The steel sheet having an average r-value of at least 1.2, an r-value in the rolling direction of at least 1.3, an r-value in the direction of 45 degrees to the rolling direction of at least 0.9, and an r-value in the direction of a right angle to the rolling direction of at least 1.2.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS[0001]This application is a division of U.S. patent application Ser. No. 10 / 487,797 filed on Feb. 24, 2004 as a national stage application of PCT Application No. PCT / JP02 / 006518, which was filed on Jun. 27, 2002, and published on Mar. 6, 2003 as International Publication No. WO 03 / 018857 (the “International Application”). This application, like U.S. patent application Ser. No. 10 / 487,797, claims priority from the International Application pursuant to 35 U.S.C. § 365. The present application also claims priority under 35 U.S.C. § 119 from Japanese Patent Application Nos. 2001-255384, 2001-255385 and 2002-153030, filed on Aug. 24, 2001, Aug. 24, 2001 and May 27, 2002, respectively, the entire disclosures of which are incorporated herein by reference.TECHNICAL FIELD OF THE INVENTION[0002]The present invention relates to a steel sheet excellent in workability used for panels, undercarriage components, structural members and the like of an automobil...

Claims

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Application Information

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Patent Type & Authority Applications(United States)
IPC IPC(8): C22C38/02C22C38/04C22C38/06C21D8/02C21D8/04C21D9/48C22C38/00
CPCC21D8/0226C21D8/0236C21D8/04C21D9/48C21D2211/002C21D2211/008C25D5/34C22C38/002C22C38/02C22C38/04C22C38/06C23C2/02C22C38/001C23C2/024C23C2/0224
Inventor YOSHINAGA, NAOKIFUJITA, NOBUHIROTAKAHASHI, MANABUHASHIMOTO, KOJISAKAMOTO, SHINYAKAWASAKI, KAORUSHINOHARA, YASUHIROSENUMA, TAKEHIDE
Owner NIPPON STEEL CORP
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